Drug Concentration, Immunogenicity, and Efficacy Study in Patients With Rheumatoid Arthritis Currently Treated With Etanercept, Adalimumab, or Infliximab: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Drug Concentration, Immunogenicity, and Efficacy Study in Patients With Rheumatoid Arthritis Currently Treated With Etanercept, Adalimumab, or Infliximab (NCT01981473), a registered phase not stated study. The primary outcome is Percentage of Participants Positive for Antidrug Antibodies Among Those Treated With Etanercept Versus Those Treated With Monoclonal Antibodies (Adalimumab or Infliximab)..

2. Clinical Question

The registry frames the study around relationships between antidrug antibodies, serum drug concentrations, and clinical response in rheumatoid arthritis. It also lists disease activity and function measures, including DAS28, CDAI, SDAI, DAS28-CRP, and HAQ-DI. These additional measures help describe the clinical characteristics considered alongside antibody status, but their presence does not establish that antibody positivity caused any observed difference.

The comparison concerns people who had already been receiving their treatments; it is not a comparison of assigned treatment strategies. The record does not report the primary comparison's observed percentages, group-level antibody counts, or a measure of uncertainty. Thus the question is identifiable, but the posted information does not establish the direction or magnitude of an answer.

3. Trial Design

NCT01981473 is a completed study sponsored by Pfizer. The registry lists enrollment of 605 and gives a start of 2014-01 and primary completion of 2014-12. The condition is rheumatoid arthritis. The study title and brief description concern drug concentration, immunogenicity, and efficacy among people receiving etanercept, adalimumab, or infliximab.

The design described by the record is an assessment of participants already receiving these treatments in clinical practice. The arm descriptions specify that participants had been receiving their respective treatment for a minimum of 6 months and maximum of 24 months before the assessment visit. The interventions are recorded as no intervention. Treatment was therefore not assigned as a study intervention in the description, and the record does not establish that participants were randomized. Allocation is not stated.

The primary outcome compares the percentage positive for antidrug antibodies among participants receiving etanercept with the percentage among participants receiving adalimumab or infliximab, grouped as monoclonal antibodies. Secondary outcomes include antibody positivity by treatment, serum trough concentrations by antibody status, and disease activity or function measures by antibody status. The secondary outcomes also include low disease activity, defined using DAS28 ESR score ≤ 3.2.

The primary assessment timeframe is 1 day, while treatment exposure before assessment spans 6 months to 24 months. The record does not describe a follow-up schedule beyond the stated assessment, nor does it report how participants were selected from clinical settings, how antibody status was measured, or whether any covariates were used in analysis. Those design details are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Participants treated with one of the three targeted therapies were enrolled using interactive response technology to assure data for approximately 200 participants were included for each RA treatment.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: FAS included participants who were diagnosed of RA and who received continuous treatment with either etanercept, adalimumab, or infliximab for a minimum of 6 months to 24 months prior to study assessment visit.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: The full analysis set (FAS) composed of participants who had diagnosis of RA and who received treatment with etanercept, adalimumab, or infliximab for a minimum of 6 months and a maximum of 24 months prior to the study visit. Data was not collected or analyzed on participants who entered the study but did not complete based on not meeting criteria.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants Positive for Antidrug Antibodies Among Those Treated With Etanercept Versus Those Treated With Monoclonal Antibodies (Adalimumab or Infliximab)., measured over 1 day.

The primary endpoint is the percentage of participants positive for antidrug antibodies among those treated with etanercept compared with those treated with adalimumab or infliximab. It is a binary outcome summarized as a percentage: each participant is classified as antibody-positive or not positive under the study's assessment, and the percentage describes how frequently positivity was observed within a treatment group. The exact laboratory threshold and assay procedures are not reported in the registry record.

This outcome is used to describe immunogenicity in the treatment groups and to address the study's stated question about whether antibody positivity differs between etanercept and the two monoclonal antibodies considered together. The brief study description also raises relationships with serum drug concentration and clinical response. An antibody-positive percentage alone, however, does not measure drug concentration or clinical response, and it does not establish that antibodies caused a change in either.

The endpoint description specifies a 1-day timeframe. The population is described as people with rheumatoid arthritis who had received continuous treatment for 6 months to 24 months before the assessment visit. The registry record does not report the observed group percentages, positive counts, confidence intervals, or a p-value for this primary endpoint. Consequently, the endpoint's definition is available, but its estimated result and precision are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary classification summarized as a percentage of participants. In general, a percentage for a binary outcome depends on the count meeting the outcome definition and the relevant denominator. For this study, that means the number classified as antidrug-antibody positive relative to the number assessed in each treatment group. The registry record does not report those primary counts or denominators, so no group percentage can be described from the posted results.

What does the comparison estimate?

The stated primary contrast compares etanercept with adalimumab or infliximab combined. This is distinct from comparing all three treatments separately, and it is also distinct from comparing antibody-positive with antibody-negative participants. The secondary outcomes include both kinds of questions: positivity by treatment, and clinical or drug-concentration measures by antibody status. Keeping the comparison groups clear matters because each contrast has its own interpretation and denominator.

In general, an unadjusted comparison of percentages describes the observed groups without accounting for other participant characteristics. An adjusted analysis can attempt to account for measured characteristics, but its interpretation depends on the variables included and the model used. The registry record does not report whether the primary comparison was adjusted, which statistical test or model was used, or how any adjustment variables were selected. No particular analytical method should therefore be attributed to the investigators.

How should uncertainty be understood?

In general, sampling uncertainty means that an estimate from a group of participants may differ from the value that would be observed in a broader population. A confidence interval expresses uncertainty around an estimate under the assumptions of the analysis. For a percentage or a difference between percentages, the interval's width depends on the amount of information and the analysis method. The registry record does not report a confidence interval or other uncertainty measure for the primary endpoint. Without the result and its uncertainty, the magnitude and precision of the comparison cannot be evaluated.

A p-value, in general, is a measure of how compatible the observed data are with a specified statistical null model. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The primary p-value and the testing procedure are not reported in the registry record. A statistical significance claim is therefore not available from this information.

Why might over-dispersion matter?

In general, over-dispersion occurs when outcome variability is greater than a statistical model assumes. If a model assumes a level of variability that is too small, standard errors may be understated and uncertainty may appear too low. This issue can arise in some grouped or count-based settings, but the registry describes a percentage endpoint and does not state that a model susceptible to over-dispersion was used. It would be inappropriate to claim that over-dispersion occurred in this study; the concept is relevant only as a general modeling consideration.

Likewise, general guidance about modeling does not identify the approach actually used. The record does not report the laboratory assay, positivity threshold, handling of borderline results, or whether repeated measurements were available. Those details could affect the definition and reliability of antibody status, but they are not reported in the registry record.

What do the planning illustrations mean?

Any sample-size figures associated with these results are planning illustrations computed from an observed effect under stated assumptions. The assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is expressed as a stated fraction of the observed effect. For this binary outcome, such illustrations are participants per arm for a specified power. They do not describe the trial's original design or demonstrate observed power. The registry record does not report the trial's own sample-size justification, and the planning assumptions should not be mistaken for its protocol.

In general, power is a design quantity: it describes the chance that a specified procedure detects an effect of a chosen size under assumed conditions. It is not a measure of whether a completed study has produced reliable or important findings. A planning calculation based on an observed effect is especially dependent on that estimate and its uncertainty. Because the primary endpoint results are not reported in the registry record, the illustrations cannot supply a missing primary result.

The registry lists 12 outcome measures and 1 analysis. That count alone does not explain the statistical plan, identify which outcomes were tested together, or show how uncertainty was handled. The methods, testing hierarchy, and any adjustments for multiple comparisons are not reported in the registry record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Etanercept", "Adalimumab/ Infliximab")
n      <- c(200, 394)
events <- c(0, 96)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Etanercept  200  0  0.0  0.0  1.8  0.0  1.9  0.0  1.8
ARM  Adalimumab/ Infliximab  394  96  24.4  20.2  28.9  20.4  28.8  20.4  28.8

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 12 outcome measures, including the primary antibody-positive percentage and secondary measures concerning antibody status, drug concentration, disease activity, and function. It also lists 1 analysis. These counts do not reveal whether outcomes were tested as a single family, whether a hierarchy was prespecified, or whether any multiplicity adjustment was used. The statistical plan for multiple comparisons is not reported in the registry record.

In general, when many statistical hypotheses are tested, the chance of at least one apparently unusual result can increase if each is assessed separately without adjustment. Methods for controlling this issue depend on the objectives and analysis plan. The outcome list alone cannot establish which approach, if any, applied. Since outcome results and p-values are not reported in the registry record, the consequences of multiplicity cannot be assessed.

The primary population is described as the full analysis set, consisting of participants diagnosed with rheumatoid arthritis who received continuous treatment with one of the three medicines for 6 months to 24 months before assessment. The record does not report how many participants from the enrollment were included in that set, how many had evaluable antibody tests, or whether the population definition was applied differently across outcomes.

Missing-data methods are also not described. The record does not state how missing antibody tests, incomplete disease-activity scores, or unavailable drug-concentration measurements were handled. It does not report exclusions, imputation, or sensitivity analyses for missing outcomes. These omissions limit assessment of how representative the analyzed participants were of the stated study population and how robust any outcome estimate might be.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: blood count abnormal (0.5%), renal failure (0.5%).

The adverse-event record reports serious events and other events separately for each treatment group. For etanercept, 200 participants were at risk for each category; 1 had a serious event and 5 had another event. For adalimumab, 199 were at risk for each category; 0 had a serious event and 4 had another event. For infliximab, 196 were at risk for each category; 1 had a serious event and 11 had another event. These are reported counts, not percentages calculated from the group denominators.

The registry also lists Blood Count Abnormal and Renal Failure among the top serious terms, each at 0.5%. The record does not establish a treatment-group attribution for those terms in the information. Death counts are not reported in the registry record.

These figures describe events recorded in the study groups; they do not establish that a treatment caused an event or permit a causal safety comparison. The groups were not described as randomized, and the registry record does not report event definitions, ascertainment procedures, follow-up time for safety, or a statistical comparison of event rates. The at-risk counts for safety should not be substituted for the primary endpoint denominators.

13. What the Result Does, and Does Not, Mean

The record identifies an observational assessment of antidrug-antibody positivity among people with rheumatoid arthritis already receiving etanercept, adalimumab, or infliximab. Its primary question is a comparison between etanercept and adalimumab or infliximab combined. The stated study objective also connects antibody status with drug concentration and clinical response, while the secondary outcome list names measures intended to describe those domains.

What the record does not establish is the primary result. The antibody-positive percentages and counts, their uncertainty, and the inferential analysis are not reported in the registry record. It is therefore not possible to state which group had a higher percentage, how large any difference was, or how precisely it was estimated. The title and objective are not evidence of an outcome.

Even if a difference in antibody positivity were reported, this design would not by itself show that treatment caused the difference. Participants were receiving treatments in clinical settings, and no study intervention was specified. Allocation is not stated, and the groups are not a like-for-like randomized control comparison. Differences in participant characteristics or treatment selection could affect an observational comparison; the registry record does not report an adjustment strategy that would address this.

Antibody positivity is also not interchangeable with serum drug concentration, disease activity, function, or a clinical response. The secondary outcomes name these distinct measures, but their results are not reported in the registry record. A finding in one domain would not automatically establish a finding in another.

The enrollment figure of 605 describes the study enrollment, not necessarily the number contributing to each endpoint. Without analyzed group denominators and missing-data details, the primary estimate's representativeness cannot be evaluated. The appropriate reading is consequently narrow: the registry defines a useful association question and describes the groups and outcomes, but it does not provide the primary result needed to quantify the comparison.

14. Why This Trial Matters Statistically

This study is statistically notable for the distinction between an association question and a treatment-effect question. It examines antibody status among people already receiving medicines in clinical practice, rather than describing random assignment to treatment. The primary comparison can therefore characterize observed group differences, but interpretation as a causal effect would require design and analysis support not described in the registry record.

The record also makes clear why outcome definitions and denominators matter. A percentage is interpretable only with a clear outcome classification and a population denominator. Here, the primary endpoint is defined as the percentage positive for antidrug antibodies, and the treatment exposure window is described. However, the observed counts and denominators for that endpoint are not reported. Enrollment alone cannot fill that gap.

Multiple outcome domains are identified: immunogenicity, drug concentration, disease activity, and function. These are related research questions, but they are not interchangeable outcomes. Their interpretation depends on which contrast is made, which participants contribute data, and how uncertainty is handled. The registry lists 12 outcome measures but does not report the multiplicity strategy or the detailed statistical methods.

The case also illustrates the limits of planning calculations based on an observed effect. Such values are planning illustrations under explicit assumptions, not observed power and not evidence that the original study was designed to detect a particular effect. The registry record does not report its own sample-size justification.

For clinical researchers, the central statistical lesson is to separate a clearly stated research question from a fully reported result. Study aims and outcome definitions support understanding of what was investigated, while estimates, denominators, uncertainty, and methods are needed to evaluate what the data show. Those primary result details are not reported in the registry record.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The main limitation for interpreting the primary question is that its observed result is not reported in the registry record. There are no primary antibody-positive counts or percentages, group denominators, confidence intervals, or p-values in the information described. The direction and magnitude of the comparison therefore remain unknown.

The treatment groups reflect existing clinical treatment, and the record specifies no intervention. Allocation is not stated, and the comparison is not described as randomized. The record does not report participant characteristics by group, reasons for treatment selection, potential confounders, or an adjusted analysis. Any treatment-group difference would therefore need cautious interpretation as an association rather than an established treatment effect.

Details about antibody measurement are not reported: the assay, positivity threshold, handling of indeterminate results, and timing relative to treatment or dosing are unspecified. The primary timeframe is 1 day, but that does not by itself describe the full timing of blood collection or any repeated assessments. The record also does not report the statistical test or model used.

The enrolled population and analyzed population may not be identical. Although enrollment is listed as 605 and the full analysis set is described, group-level primary denominators, exclusions, and missing outcome counts are not reported. Missing-data handling and sensitivity analyses are also not reported.

Finally, 12 outcome measures are listed, but the registry record does not describe a prespecified testing hierarchy or multiplicity control. The safety figures provide counts, but the event definitions, ascertainment procedures, and safety follow-up are not reported. Together, these gaps restrict assessment of precision, comparability, and robustness.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Drug Concentration, Immunogenicity, and Efficacy Study in Patients With Rheumatoid Arthritis Currently Treated With Etanercept, Adalimumab, or Infliximab — NCT01981473.
• Registry record last updated 2016-01-12; status last verified 2015-12.
• Results first posted 2016-01-12.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT01981473 is a completed Pfizer-sponsored study of people with rheumatoid arthritis receiving etanercept, adalimumab, or infliximab. The registry lists enrollment of 605, a start of 2014-01, and primary completion of 2014-12. Participants had received their current treatment for 6 months to 24 months before assessment, and the interventions are recorded as no intervention.

The primary endpoint compares the percentage positive for antidrug antibodies among etanercept recipients with the percentage among adalimumab or infliximab recipients combined. Secondary measures address antibody status, serum trough concentrations, disease activity, and function. Safety counts are reported by treatment group.

The registry record does not report the primary outcome estimates or their uncertainty. It also does not report detailed statistical methods, missing-data handling, or a multiplicity plan. The available record therefore defines the research question and study context but does not allow the primary comparison's result or precision to be assessed.